feat: tickets I follow, and more news for followers

"Que sigo" on the home page lists the open tickets I follow, whoever
works on them; `watching` filters my issues (REST, GraphQL, MCP) and a
project's search (none without a session).

Followers now also hear when a ticket's priority or due date changes,
and when it enters or leaves a sprint. Smaller edits (title, labels…)
still do not notify.

Docs (with the REPLIED row the replies change missed), Word and PDF
updated.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/tracker/domain/src/lib/models/inputs.ts

@@ -72,6 +72,8 @@ export interface CreateReleaseInput {
 export interface MyIssuesFilter {
   /** true: assigned to me. false: any ticket of my projects. */
   assignedToMe: boolean;
+  /** Only the tickets I follow. */
+  watching?: boolean;
   categories?: StatusCategory[];
   /** Matches key, title or description. */
   search?: string;